The present invention relates to tractor trailer parking brake control.
The application and release of tractor and trailer parking brakes has normally been accomplished using separate manual controls which apply air pressure to or vent air from the lines controlling the respective parking brake systems. The line controlling the trailer system normally controls an intermediate tractor protection valve. The tractor protection valve cuts off the lines to the trailer in case of trailer breakaway to prevent catastrophic loss of air pressure from the tractor.
A total of three parking brake control valves has been required in order to give individual control of tractor and trailer parking brakes as well as single knob application of both tractor and trailer parking brakes. Individual control has been desired in order to retain the tractor parking brakes set while charging the trailer brake system and for setting the trailer parking brakes without setting the tractor brakes. Such an arrangement unfortunately may allow a dangerous condition to occur by permitting the tractor parking brake to be applied without simultaneously applying the trailer parking brakes. If such an application of tractor parking brakes alone should occur during motion of the vehicle, dangerous jackknifing of the trailer may result.